1. Technical Field
The present invention relates to a flatbed scanner, and more particularly, to a method and apparatus for correcting a scanning error due to a deviation in the position of a charge-coupled device (CCD) module of a flatbed scanner.
2. Description of the Related Art
In a flatbed scanner, a CCD module emits light onto a transparent glass of a flatbed, focuses light reflected from a document that sits on the transparent glass, and reads the image of the document. To accomplish this, upon application of power to the flatbed scanner, the CCD module moves until a home position is detected. If the home position is detected, the CCD module moves to a white shading plate in order to set white shading. Then, if the white shading is set through a white shading plate, the CCD module moves to a scan start line of the transparent glass in order to start an actual scanning operation.
A conventional flatbed scanner moves the CCD module to the home position using a home position sensor provided therein. The flatbed scanner controls other movements of the CCD module, i.e., the movements of the CCD module from the home position to the white shading plate and from the white shading plate to the scan start line, by using values which are pre-computed considering the distances the CCD module is to be moved.
However, since the pre-computed values do not vary depending on the type of flatbed scanner but are determined from a standard flatbed scanner, any deviations in the movement of the CCD module may cause distortions in a resultant image.
For example, if deviations in the position of the CCD module occur such that the scan start line is not detected exactly, Y-registration may occur such that a vertical line, which does not exist in a real image, exists at the top of the scanned image. Furthermore, since a conventional flatbed scanner operates to set the position of a first pixel on a document at a predetermined value, for example, 130 pixels, if an image is scanned such that the first pixel is positioned in front of the predetermined value due to a deviation in the position of the CCD module, the content of the document in front of the predetermined value is shielded by a scan-upper to produce a vertical line that does not exist in the real image on the left portion of the document.
Furthermore, a conventional flatbed scanner does not consider a skew that results when the CCD module is slanted to the right or left, thereby obtaining an unexpected scanned image due to skew of CCD module.
In addition, a conventional flatbed scanner does not consider the right and left magnifications of a scanning image, thereby failing to obtain a scanning image having an accurate scan rate due to a scanning deviation of a CCD module. For example, even if an image having a scan rate of 100% is desired, an image having a scan rate of 105% or 95% may result.